The needs are rising for tests and analyses of semiconductor devices that are becoming progressively minute. In failure analyses for specifying the cause of failure, in particular, the direct observation of defects within devices has become an indispensable technology. For these observations, it is necessary to precisely microfabricate the position of observation objects of the device. So far, this precise miocrofabrication has been carried out by means of a tool called “focused ion beam (hereinafter referred to as “FIB”) processing device.” As this FIB enables to work precisely on the target position by irradiating the specimen with ion beam focused to the submicron order and electrostatically deflecting the same, this is used for shaping the section for analysis and for fabricating specimens for analysis.
And in this failure analysis processing, the needs are rising for fabricating specimens for analysis in a short period of time. As an improvement in yield is directly connected with the device cost, the identification of the cause of the failure in a short period of time will have a great impact on the reduction of cost. Therefore, a rapid processing of specimens for analysis is expected. As a processing device for realizing this, there is, for example, a projection ion beam (hereinafter referred to as “PJIB”) processing device described in JP-B No. 3542140. Unlike the FIB processing device described above that processes to shape the intended form by focusing, deflecting ion beams and scanning the specimen with the same, this device enables to process the specimens in block by projecting mask patterns of shapes similar to the intended shapes predetermined in advance on the specimen. The processing speed is determined roughly by how much ions are irradiated on the area to be processed. In other words, the larger the ion beam current is, higher the processing speed rises. In terms of simple ion beam current density in the ion diameter, the FIB is greater than the PJIB. However, in the processing of an area where the PJIB ion beam current is greater than the FIB ion beam current, the PJIB processing is simply faster. In fact, in the case of processing used for the failure analysis of devices, there is hardly any processing in the submicron range, and in most cases processing in the range of several to several tens of microns is required. And in such cases, the PJIB processing has the merit of being faster.
Since the analyses of failures by using these apparatus for ion beam fabrications were often conducted in the past by specialized operators, even if an anomalous event has occurred in the device, it was possible to cope with such an event by the skill of the operators. Lately however, devices capable of automatically processing without the attendance of any specialized operator have increased. As a result, it has become important to secure the stability of beams in particular in these devices. In order to secure stability of beams, it is effective to monitor beams. For example, JP-B No. 3567749 describes an example of the method of monitoring beam current by an ion implantation equipment. This describes the method of measuring the distribution of current at two points before and after the item processed by means of multipoint Faraday cups, and interpolating or extrapolating the current density distribution of ion beams at the position of the processed item (specimen). It also states that, in view of such a presumed current density distribution, the distribution of beams can be compensated by for example extending the scanning irradiation time in an area with a low current density and by curtailing the scanning irradiation time in an area with a high current density.